Why Can't I Use `bindParam` with Constant Values in PDO?

Can't Pass Parameter By Reference with bindParam for Constant Values?

When working with PDO, you may encounter the error "Cannot pass parameter 2 by reference" when using bindParam with constant values. Here's why and how to resolve it:

The Issue

bindParam expects a variable to bind as a reference, not a constant value. Constant values like null, '' (empty string), or PDO::PARAM_NULL cannot be passed by reference.

The Solution

To bind constant values, use bindValue instead of bindParam. bindValue accepts a literal value without passing it by reference. The following code uses bindValue to insert a NULL value:

$stmt->bindValue(':v1', null, PDO::PARAM_NULL);

Note:

• bindParam requires a variable because it creates a reference to the variable's value.
• bindValue does not create a reference and accepts a constant value directly.
• PDO::PARAM_NULL cannot be used with bindValue.

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